1. Field of the Invention
The present invention relates to semiconductor lasers.
2. Description of the Related Art
International Publication No. WO2003-012936 (referred to as “Patent Document 1” hereinafter) and Yuliya A. Akulova et al., “Widely Tunable Electroabsorption Modulated Sampled-Grating DBR Laser Transmitter”, IEEE Journal of Selected Topics in Quantum Electronics, Vol. 8, No. 6, pp. 1349-1357 (2002) (referred to as “Non-Patent Document 1” hereinafter) each disclose a wavelength tunable semiconductor laser with distributed Bragg reflectors (DBR) disposed on opposite sides of a gain region.
The semiconductor laser discussed in Patent Document 1 includes two distributed Bragg reflectors, one of which having a chirped diffraction grating whose grating pitch varies in a light propagation direction and a plurality of electrodes arranged in the light propagation direction. In this semiconductor laser, light having a desired wavelength is reflected by applying current selectively to the plurality of electrodes formed in the one distributed Bragg reflector. The other distributed Bragg reflector has another diffraction grating having a plurality of reflection peaks in a reflection spectrum. When wavelengths at reflection peaks of the two distributed Bragg reflectors overlap each other, laser oscillation occurs at the aforementioned wavelength. The oscillation wavelength can be changed by adjusting the current applied to the corresponding electrode formed in the one distributed Bragg reflector.
In the semiconductor laser discussed in Non-Patent Document 1, two distributed Bragg reflectors have a sampled-grating (SG) structure. In this semiconductor laser, the oscillation wavelength can be changed by controlling the current individually applied to the two distributed Bragg reflectors.